1. Field of the Invention
The present invention relates to swash plate type compressors suitable for air-conditioning of vehicles, and more particularly to a technique for preventing the sliding surfaces of the swash plate and the piston webs in such a compressor from becoming excessively worn.
2. Description of the Prior Art
In a swash plate type compressor, pistons reciprocating in cylinder bores are mounted over a swash plate which is fixedly secured to a drive shaft in such a manner as to be slanting with respect to the drive shaft. The pistons are coupled to the swash plate through bearing means comprising shoes and balls. Furthermore, in general, as shown in FIG. 6, a sliding surface or contact surface 20 of each piston web 19, which confronts a circumferential surface of the swash plate, has a curvature substantially equal to that of the circumferential surface of the swash plate. When the swash plate 22 rotates in the direction of the arrow P in FIG. 6, because of the rotational movement of the piston 16 caused by the rotation of the shoes 23 and the balls 24, the piston web 19 which is positioned at the rear side in the direction of rotation of the swash plate 22, i.e., the left-hand piston web 19 in FIG. 6, is more forcefully brought into contact with the circumferential surface of the swash plate. In this case, the outer portion of the piston web 19 contacts the circumferential surface of the swash plate as shown in FIG. 7(a), or the inner portion contacts it as shown in FIG. 7(b). In the former case as shown in FIG. 7(a), a wedge effect can be obtained during the period of initial use after the compressor has been assembled. However, as the piston web is worn, the wedge effect is eliminated. On the other hand, in the latter case where the inner portion contacts with the circumferential surface of the swash plate, no wedge effect can be obtained, and the rotational movement of the piston cannot be sufficiently supported.
Thus, in the conventional swash plate type compressor, the sliding surfaces of the piston webs, which are slidably brought into contact with the circumferential surface of the swash plate, are not sufficiently lubricated, as a result of which metal contact takes places to quickly wear these components. In particular, when the swash plate and the pistons are made of aluminum, they are worn very fast.